1. Field of the Invention
This invention relates to a motor vehicle drive system controller, particularly to a motor vehicle drive system controller of the type adapted to controlling the operation of the automatic drive system to optimize the running speed of a motor vehicle by controlling the power output of the engine or the electric motor and controlling the gear selection of the automatic transmission according to a set of given parameters.
2. Description of the Related Art
Demand for automatic motor vehicle drive systems that can effectively reduce the physical and psychological load on the part of the driver by automatically controlling some of the operations of driving the motor vehicle for the driver has increased. Currently available motor vehicle drive system controllers are mostly designed to control the running speed of the motor vehicle by controlling the opening of the engine throttle valve. On the other hand, motor vehicle drive system controllers designed to control the running speed of the motor vehicle by controlling not only the opening of the engine throttle valve, but also the gear-shifting operation of the automatic transmission have been proposed and commercialized with some success.
An automatic drive controller is typically either of a constant speed type or of a follower type. A constant speed type automatic drive controller controls the motor vehicle drive system including the engine in such a way that the motor vehicle is constantly driven to run at an intended speed. On the other hand, with a follower type automatic drive controller, the motor vehicle is made to follow an arbitrarily selected preceding vehicle, constantly maintaining a given distance from that vehicle. The arbitrarily selected lead vehicle is also called a target vehicle. Automatic drive controllers that can operate both in a constant speed mode and in a follower mode have also been proposed. With such a controller, the motor vehicle is driven to move at a constant speed until a target vehicle is caught in sight, when the automatic vehicle drive operation is switched to the follower mode.
A follower type controller determines the distance separating the leading vehicle and itself by means of a radar and then calculates a desired inter-vehicular distance for the follower on the basis of the speed of the leading vehicle detected by a speed sensor. The motor vehicle drive system is then so controlled as to make the actual inter-vehicular distance agree with the desired value. The motor vehicle may have to adapt itself to sudden deceleration of the leading vehicle and a motor vehicle suddenly intervening between the leading vehicle and the following vehicle. The automatic transmission then shifts gears down and the follower vehicle is decelerated by the braking effect of the engine. Japanese Patent Laid-Open Publication No. Hei 6-11200 discloses an automatic drive controller that determines the inter-vehicular distance between the leading vehicle and the following vehicle by means of a laser radar and, once a shortened distance is detected, causes the automatic transmission to downshift gears to decelerate the motor vehicle.
Japanese Patent Laid-Open Publication No. Hei 4-208647 teaches an automatic drive controller for controlling the automatic transmission so as to cause it to appropriately shift gears and drive the motor vehicle at a constant running speed. The controller shown in that publication causes the automatic transmission to shift gears down for accelerating the moving vehicle and up when the target speed is achieved. Japanese Patent Laid-Open Publication No. Hei 7-304349 also described an automatic drive controller for driving a motor vehicle at a constant running speed by controlling the operation of the automatic transmission.
In a related technological field, a control apparatus for regulating the running speed of a motor vehicle by locking up the torque convert apparatus is disclosed by the applicant of the present patent application in Japanese Patent Application No. Hei 8-147084. With this apparatus, a lock-up clutch arranged in parallel with the torque converter is engaged to produce a locked-up state or a locked-up slipping state whenever necessary in order to realize an enhanced level of deceleration.
A motor vehicle is driven by the motor vehicle drive system either in a drivable mode or in an undrivable mode as shown in FIG. 1 of the accompanying drawings, which is a graph schematically illustrating the relationship between the engine torque T (axis of ordinate) and the running speed v (axis of abscissa) of the motor vehicle. In the drivable mode, the drive force of the motor vehicle engine exceeds the running resistance of the motor vehicle (hereinafter referred simply as Is "running resistance") and the engine is positively driving the motor vehicle. On the other hand, in the undrivable mode the drive force of the engine falls below the running resistance and the motor vehicle may be decelerated by the braking effect of the engine.
The gear-shifting operation of the automatic transmission is controlled differently in the drivable mode and in the undrivable mode. This difference may be attributable to the structural requirements of the transmission, as will be described in greater detail hereinafter, or to the requirement of alleviating the impact at the time of shifting gears and improving the driver's comfort in the running motor vehicle. Thus, the automatic drive controller is required to determine if the motor vehicle is in a drivable mode or in an undrivable mode at the time of shifting gears in order to properly control the automatic transmission. This operation of finding out the driving mode on the part of the automatic drive controller is typically carried out on the basis of the throttle opening and the running speed of the motor vehicle detected by the speedometer as shown in FIG. 2. In FIG. 2, the axis of abscissa and that of ordinate respectively represent the motor vehicle running speed v and the throttle opening .theta.. The solid curve in FIG. 2 indicates the reference running resistance or the reference resistive throttle opening of the engine, which is determined by converting the running resistance of FIG. 1 into the throttle opening according to a predetermined relationship between the engine torque and the throttle opening. Then, the mode of operation of the engine is determined by comparing the detected throttle opening .theta. and the reference resistive throttle opening for the detected running speed of the motor vehicle.
A typical situation where the operation of shifting gears is carried out by the automatic drive controller while determining if the motor vehicle running in a drivable mode or in an undrivable mode is when the running motor vehicle needs to be quickly decelerated while it is following a target vehicle. In such a situation, the gears must be shifted the instant when such deceleration is determined necessary. Thus, when deceleration is requested and it is detected that the motor vehicle is running in a drivable mode, the gear-shifting operation has to be controlled in a manner adapted to the drivable mode. When, on the other hand, deceleration is requested and the motor vehicle is found to be running in an undrivable mode, the gear-shifting operation has to be so controlled as to adapt itself to the undrivable mode. The throttle may have to be simultaneously closed, totally if necessary, for further deceleration.
[Example situation in which the gear-shifting operation has to be conducted differently in drivable and undrivable modes]
A situation where the gear-shifting operation has to be conducted differently in the drivable mode and in the undrivable mode will now be described by way of an example.
FIG. 3 is a schematic diagram of an automatic transmission described in Japanese Patent Laid-Open Publication No. Hei 6-341522 and FIG. 4 is an operation chart of the frictional engaging devices of the automatic transmission for different gear positions. Referring to FIG. 3, the automatic transmission includes a 5-step transmission gear mechanism and a hydraulic control unit for controlling the operation of the transmission gear mechanism. It comprises an auxiliary transmission OD including a front overdrive planetary gear unit in combination with a main transmission M for 4-step forward drive and 1-step rearward drive including a simply linked train of three planetary gears.
The automatic transmission comprises, in addition to the auxiliary transmission OD and the main transmission M as listed above, a torque converter T having a lock-up clutch. The auxiliary transmission OD is provided with a first one-way clutch F-0 and a multi-disc clutch C-0 arranged in parallel and associated with a sun gear S0, a carrier C0 and a ring gear RO, along with a multi-disc brake B-0 connected in series with the first one-way clutch C-0. On the other hand, the main transmission M comprises three sets of simply linked planetary gear units P1, P2 and P3 realized by appropriately and directly connecting various transmission elements including sun gears S1-S3, carriers C1-C3 and ring gears R1-R3. There are also provided multi-disc clutches C-1, C-2, a band brake B-1, multi-disc brakes B-2 through B4, a one-way clutch F-1 and a second one-way clutch F-2 in association with the transmission elements of each of the gear units. Additionally, each of the clutches and the brakes is provided with a servo system (not shown) having a piston for engaging/disengaging its frictional members that is controlled under servo hydraulic pressure.
Now, assume that the top (5th) gear must be shifted down to the 4th gear and this gear-shifting operation must be conducted differently in a drivable mode and in an undrivable mode. Note that the sense of rotation of the automatic transmission as described herein represents the one as viewed from the engine side.
With the above described automatic transmission, the rotary power output of the engine (not shown) is transmitted to the input shaft I of the auxiliary transmission OD. Referring now to FIG. 4, the 4th gear is selected when the clutch C-0 is engaged to fix the auxiliary transmission OD, while the clutches C-1 and C-2 of the main transmission M are engaged, and all the remaining frictional engaging members are disengaged. The gear unit P2 is directly linked under this condition because the rotary power input is transmitted to the ring gear R2 and the sun gear S2. In other words, the rotary power input is simply output by the automatic transmission. It will be understood that the motor vehicle is constantly subjected to the braking effect of the engine when the vehicle is driven to run by the axle (and hence in an undrivable mode) under this condition. When the main transmission is in the 4th gear, the clutch C-0 is disengaged and the brake B-0 is made operative in the auxiliary transmission OD to realize a shift to the top gear. In the top gear the sun gear S0 is locked and rotating speed increase at the auxiliary transmission OD.
For the downward gear-shifting operation from the top gear to the 4th gear with the above automatic transmission, the brake B-0 is released and the clutch C-0 is engaged. If the motor vehicle is running in a drivable mode when the brake B-0 is released, the sun gear S0 attempts to rotate clockwise relative to the carrier C0. This rotary motion is blocked by the one-way clutch F-0. In other words, as the brake B-0 is released, both the carrier C0 and the sun gear S0 rotate under the effect of the one-way clutch F-0. Considering this functional configuration, it is so arranged with this automatic transmission that the timing of gear shifting operation is controlled by the one-way clutch F-0 in the drivable mode.
If, on the other hand, the brake B-0 is released in an undrivable mode, the sun gear S0 tries to rotate counterclockwise relative to the carrier C0. This rotary motion is not blocked by the one-way clutch F-0. In other words, the timing of gear shifting operation is not controlled by the one-way clutch F-0 in the undrivable mode and the impact of gear shifting operation is alleviated exclusively by controlling the pressure under which the clutch C-0 is engaged.
Thus, with an automatic transmission as illustrated in FIG. 3, the downward gear shifting operation from the top gear to the 4th gear differs in the drivable and undrivable modes and this difference normally occurs with any other gear shifting operations and also with any automatic transmissions having a configuration different from the one illustrated in FIG. 3. Note, however, that a gear shifting operation may be conducted differently in the drivable mode and in the undrivable mode even if such a difference is not structurally required. Gear shifting operations for other than the 4th and top gears may be understood by referring to FIG. 4 and hence will not be further described.
Gear shifting operations without relying on an automatic drive controller are performed by the driver using the accelerator and the brake, while those relying on an automatic drive controller are carried out without driver input. Thus, the driver will be more startled by a gear shifting operation relying on an automatic drive controller than by a similar operation that does not rely on the automatic drive controller. Therefore, gear shifting operation impact must be minimized when the motor vehicle is running under the control of an automatic drive controller.
Conventionally, an automatic drive controller determines if the motor vehicle is running in a drivable mode or in an undrivable mode in a manner as described above and conducts a gear shifting operation that is adapted to the determined mode. However, since the running resistance of a motor vehicle can vary as a function of not only the running speed of the vehicle, but also of the gradient, the surface conditions (the coefficient of friction of the road, etc.) on which the vehicle is running and other factors, the reference running resistance does not necessarily agree with the actual running resistance. Therefore, there always exists an ambiguous zone where whether the motor vehicle is running in a drivable mode or in an undrivable mode cannot be determined. Although it is possible to directly find out the mode of operation of the engine by means of a specifically designed detector, be it a drivable mode or an undrivable mode, installation of such an additional detector is costly and involves complex control procedures.
As described above, because there exists an ambiguous zone where it cannot be determined whether the motor vehicle is running in a drivable mode or in an undrivable mode and it is possible for the automatic drive controller to mistake a drivable mode for an undrivable mode. In such a situation, the automatic drive controller shifts gears in a manner suitable for the undrivable mode although it should operate for the drivable mode, or vice versa. Gear shifting operations not adapted to the correct mode may cause discomfort to the driver. Additionally, there may be instances where the automatic drive controller determines that the motor vehicle is running in a drivable mode and begins shifting gears in a correct manner for that mode but the mode changes during the gear shifting operation and consequently the driver is subjected to impact due to an improper gear shifting operation. Troubles of this sort should obviously be minimized.
In existing automatic drive controllers including the one disclosed in Japanese Patent Laid-Open Publication No. Hei 6-11200 referred to earlier, the transmission constitutes at least one of the objects to be controlled by the automatic drive controller. The transmission is expected to consistently operate properly and situations where the transmission fails are not taken into consideration. This will be illustrated in greater detail by way of an apparatus like the one disclosed in the above listed patent document designed for controlling both the engine and the automatic transmission in a coordinated manner.
Generally, an automatic transmission is provided with a hydraulic control unit and is actuated by the operation of a solenoid of this hydraulic control unit. If the solenoid fails, the automatic transmission would not shift gears and deceleration would not be boosted by a downward gear shifting operation. Additionally, the lock-up clutch can become uncontrollable and the engine braking effect can become unobtainable.
Thus, if the solenoid of the automatic transmission fails, the engine must be controlled so as to make up for the missing automatic transmission functionality. For example, it may be necessary to compensate for a deceleration effect normally obtained by controlling the automatic transmission by modifying the opening of the electronic throttle of the engine or the extent of fuel cut for the engine. However, such an arrangement of compensating for an automatic transmission missing function by controlling the engine can be costly and entail complex control procedures.
The above identified problem is not limited to controlling both the engine and the automatic transmission and a similar problem arises when the motive power of the motor vehicle comes from an electric motor or some other power source, or when automatic transmission and brake control are to be coordinated.